1. Field of the Invention
This invention relates to a process for recovering chlorine and obtaining iron oxide, through oxidizing roasting, from the iron chloride that is secondarily produced in the manufacture of titanium tetrachloride by chlorination of iron-containing titanium ore, e.g., ilmenite or such like titanium minerals.
2. Description of the Prior Art
Titanium tetrachloride, the starting material for producing titanium metal, chlorine-process titanium oxide, and the like, is commonly prepared in either of two ways. In one method iron and other ingredients than titanium in the ore are selectively chlorinated and evaporated by use of chlorine or other chlorinating agent to separate iron chloride and the like and obtain a high grade intermediate product rich in titanium, and then the intermediate product is further chlorinated for producing titanium tetrachloride. The other method directly chlorinates the ore to form titanium tetrachloride and iron chloride vapours together followed by separating them.
In these processes, both of which depend on chlorinating volatilization or evaporation with chlorine for the separation and recovery of titanium tetrachloride, iron chloride is inevitably produced because by nature the iron content of the titanium ore is chlorinated in preference to the titanium content.
The resulting iron chloride composition consists principally of a mixture of ferrous and ferric chlorides and the balance other chlorides originating from the ingredients included in the titanium ore, and also includes a minor proportion of coke used as the reducing agent for chlorination and carryover materials. The iron chloride has only quite limited application owing to its poor purity, and it is advantageous to oxidize it to recover chlorine gas and obtain iron oxide which may subsequently be used as a raw material for iron manufacture.
A process previously proposed for the treatment of such an iron chloride composition consists of transferring iron chloride in gaseous phase directly from the furnace for chlorinating the titanium ore into an oxidizing furnace immediately connected to the chlorinating furnace and carrying out an oxidizing treatment in the presence of oxygen in the oxidizing furnace to recover chlorine and obtain iron oxide.
The aforementioned process however has a number of shortcomings. Since the chlorinating furnace is directly connected to the oxidizing one, the other gases e.g., carbon monoxide, carbon dioxide and nitrogen are entrained in the gaseous iron chloride flow from the former furnace, and reduce the iron chloride concentration. Accordingly the concentration of the chlorine gas resulting from the oxidizing reaction of the gaseous iron chloride is also diluted. Also, because changes and shifts in the operational condition or circumstance of the chlorinating furnace usually are accompanied by fluctuations in the rate of gas production, temperature, presssure, and other working factors, it is very difficult to chose the optimum conditions under which the oxidizing reaction of iron chloride is satisfactorily effected in the oxidizing furnace; if not properly handled the iron chloride may unintendedly be discharged unreacted from the furnace. In other respects, too, the oxidizing furnace is difficult to operate as it is directly influenced by variations in the operating conditions of the chlorinating furnace.
As already noted, iron chloride is limited in its application and involves difficulties in oxidation treatment thereof. In the absence of any simple and effective technique to be employed instead, the preparation of highgrade titanium minerals or titanium tetrachloride from iron-containing titanium ores such as ilmenite by chlorination has been hampered by the secondary production of iron chloride and this has so far been a problem in the art.